The invention concerns a device for separating an uppermost sheet from a supply stack with air blowers in the area of a sheet transport unit having a sheet bending mechanism operating with a partial vacuum and feeding to a processing station in a sheet processing device.
In the case of known sheet processing devices, such as, for example, copiers, the first and second air blowers of the sheet separating device are located downstream in front of the supply stack transverse to a transport path and act opposite the sheet transport device, rising at an angle to the horizontal plane of the sheets, to the upper area of the sheet stack, which may be positioned to the same predetermined equal height by a controlled lifting device. In this case air jets are generated with low excess air pressure as well as with different directions and diameters, on the one hand for spreading by raising several sheets of the upper sheet stack area, and on the other hand for separating by raising the uppermost sheet from the stack as well as by holding back an adhering sheet following the uppermost sheet, by the first air blower supplied from a compressed air source, with an air nozzle located in the area of a center line of the stack and the transport path with several air nozzles located on both sides of the center line and the first air blower.
A device for separating by raising an uppermost sheet from a supply stack in a copier is known from EP-B1-0 812 680, in the case of which on the one hand there is a first air blower mounted centrally with respect to the sheet stack and to the sheet transport path, with an individual air nozzle having a relatively large trapezoidal opening (7.62xc3x976.35 mm to 15.24xc3x9719.90 mm) and on the other hand there is a second air blower offset in the direction of sheet transport, in each case with three air nozzles, in each case with relatively large semicircular openings (7.87 to 24.85 m2), mounted on both sides of the center line of the transport path. The alignment of the air jets with the horizontal plane of the sheets in the direction toward the upper area of the sheet stack is in an angular range between 35 to 35 degrees for the air jet of the first air blower and for the air jets of the second air blower. The excess air pressure of the air jets is around 30 mbar and is created on the air nozzles of the air blower by one or two controllable air pressure sources and maintained constant during an operating cycle.
In this case it is disadvantageous that, as a result of the large air nozzle openings and the low excess pressure of the air jets, an uppermost sheet can be separated, and transported away, from the stack only with difficulty or even not individually, in the case of using a sheet of a type of paper which is heavy, thick, or the sheets of which adhere strongly to one another. Thus the range of types of sheets of paper for reliable operation, that is, reliable separation and avoidance of double-sheet transport, is greatly limited.
Therefore the object of the invention is to create a device, which does not have these named disadvantages, but by which sheets of very different types can be reliably fed from the sheet supply stack to a sheet processing device one after the other reliably and efficiently.
The object is achieved according to the invention with a device in that an additional air blower having several nozzles, supplied by a high pressure air source, is located in the area of the center line of the stack and the transport path, by which air jets with a high excess air pressure and small diameter can be created, which on the one hand support the separation of the uppermost sheet from the stack as well as holding back the adhering sheet following the uppermost sheet, and on the other hand serve for supporting the spreading of the sheets in the upper area of the sheet stack.
Advantageously, air jets with an excess air pressure equal to or greater than 1.0 bar can be created by means of the high pressure air source and the air nozzles of the additional air blower; the pressure ratio of the air jets of the additional air blower to those of the spreading and separating means is equal to or greater than 20:1; and the ratio of the air nozzle opening diameters of the additional air blower to those of the spreading and separating air blowers is equal to or greater than 1:30. The air pressure of the air jets of the additional air blower in this case is essentially constant during an operating cycle, and the air jets of the additional air blower act on the sheets of the upper sheet stack area simultaneously with the air jets of the spreading air blower and separating means having a constant air pressure.
Furthermore, the additional blower advantageously has two nozzle elements with several air nozzles and the nozzle elements are positioned on both sides of the air blower for spreading, a first air blower, and outside the inner air nozzles of the air blower for separation and holding back, a second air blower. The additional, third air blower here in each case has two air nozzles in a vertically overlapping arrangement on the two nozzle elements, the upper air nozzles being directed toward a middle front edge area of the second and third sheets of the stack for the purpose of separating and holding back the adhering second sheet following the first stack sheet, and the lower air nozzles for supporting the spreading and lifting of the sheets located below are directed toward the middle front edge area thereof.
In addition, the air nozzles of the additional air blower, and thus their air jets, are directed advantageously parallel to the horizontal plain of the sheets of the stack and parallel to the central axis of the stack and the sheet transport path. Further features and advantages are to be deduced from the description of the embodiments of the invention shown in the drawing as well as the further subclaims.